Coupling to a bone-anchored hearing aid

ABSTRACT

The present invention refers to a coupling intended for mechanical transmission of sound information from a vibration generating apparatus as a transmitter to the skull of a person with damaged hearing, including a first coupling part, for example directly anchored to the skull, and a second coupling part attachable to it and mounted on the sender, whereby at least one vibration-transmitting surface is formed between the coupling parts.

CROSS REFERENCE TO RELATED APPLICATION(S)

The United States application stems from PCT International applicationNo. PCT/SE82/00411 filed Dec. 1, 1982.

The present invention refers to a coupling intended for mechanicaltransmission of sound information from a vibration generating apparatusas a transmitter to the skull of a person with damaged hearing,including a first coupling part, for example directly anchored to theskull, and a second coupling part attachable to it and mounted on thesender, whereby at least one vibration transmitting surface is formedbetween the coupling parts.

BACKGROUND OF THE INVENTION AND TECHNOLOGICAL STATUS

Perhaps the most common hearing damage today takes the form of defectsin the inner ear which usually are corrected with different types ofhearing aids attached to the external ear canal. Certain patients whoneed hearing aids cannot use conventional hearing aids which transmitair-borne sound through that canal but instead must use abone-conduction hearing apparatus. The reasons can be several. Forexample the hearing canal, can be defective, perhaps already from birth,so that the air-borne sound is not passed while the organs of the innerear are intact. Experience has shown that the inner ear is verysensitive to sound in the form of vibrations which are transmittedthrough the skull. A transmitter which generates sound vibrations isthen attached to the side of the head, for example using a steel springover the head, in the region of the ear and transmits sound via the headskin and bone to the inner ear. The pressure with which the transmitteris applied against the head in order to obtain as good mechanicalcontact as possible is uncomfortable for the patient. In addition theskin and tissue cause damping of the vibrations especially in the highfrequencies. During recent years through improved medical techniques onecan permanently implant a metallic skin penetration which is anchored inthe skull for transmission of sound by vibrations. Because no dampingskin is present between the sender and the skull a considerably bettersound transmission is obtained while simultaneously the electricalcurrent used by the sender can be reduced. In addition estheticimprovements have been obtained because the steel spring over the headis not needed.

A known coupling is available on the market today and is shown inFIG. 1. It includes ball-shaped and cup-shaped coupling parts of whichone, for example the ball-shaped part, is attached to the skull behindthe ear of the patient. The coupling part penetrates the skin and sticksout 4-6 mm outside the skin. To that coupling part the sender with itscup-shaped coupling part is attached with a "snap lock."

This known coupling has a number of drawbacks. For example theball-shaped coupling part sticking out of the head causes severalinconveniences. In addition to purely esthetic drawbacks clothing caneasily catch on the ball. In spite of the fact that the part of thecoupling in contact with tissue (skull bone, skin) is made of titanium,which has shown very good characteristics concerning ingrowth with thebone, the skull bone can be damaged by strong mechanical loading such asblows and the like. The problem is accentuated by the fact that thecoupling comprises a not inconsiderable lever by virtue of its largephysical height. This is also a problem during sleep when the couplingcan be in the way or catch on the bedclothes.

Other problems, such as that the coupling unscrews itself and falls out,have appeared during practical use. For example experience has shownthat the mechanical contact between the coupling parts is weakened intime which results in reduced sound quality in the transmission. This isbecause distortion results at certain frequencies and sound strengthsand the coupling parts are not able to maintain the mechanical contact.Further drawbacks are that the coupling is not provided with a "neutralposition" which means that the transmitter, which is oftenasymmetrically formed, can slip around the contact ball and lie againstthe skin which can cause interference and discomfort for the patient.

THE PURPOSE OF THE INVENTION AND ITS PRIMARY CHARACTERISTICS

The purpose of the present invention is to eliminate the aforementioneddrawbacks and to achieve a coupling which is esthetically attractive,easy to use, inexpensive to manufacture and easy to apply and repair.This is achieved thereby that the vibration transmitting surface orsurfaces of the first coupling part is/are arranged inside the outersurface of the first coupling part.

SHORT DESCRIPTION OF THE FIGURES

The invention will be described in the following in an embodiment withreference to the attached figures.

FIG. 1 shows a view, partly in cross section, of a known coupling,

FIG. 2a shows a cross section through the first coupling part of acoupling according to the invention,

FIG. 2b shows the first coupling part according to FIG. 2a from above,

FIG. 3a shows a second coupling part which fits the first coupling partshown in FIGS. 2a and 2b,

FIG. 3b shows the second coupling part, according to FIG. 3a, fromabove,

FIG. 4a shows a cross section through an alternative first couplingpart, intended to be connected to the second coupling part shown in FIG.3a,b,

FIG. 4b shows the first coupling part according to FIG. 4a, from above,

FIG. 5a shows a cross-section through a further embodiment of a couplingaccording to the invention, and more exactly its first coupling part,

FIG. 5b shows a second coupling part which fits the first coupling partshown in FIG. 5a,

FIG. 6a shows a further embodiment of a first coupling part,

FIG. 6b shows the first coupling part according to FIG. 6a, from above,

FIG. 6c shows a second coupling part which fits the first coupling partaccording to FIGS. 6a and 6b,

FIG. 7a shows a cross-section of a coupling with parts which can easilybe separated,

FIG. 7b shows an insert spacer, placed in a coupling according to 7a,from above,

FIG. 7c shows a coupling part, which fits the coupling shown in 7a, fromthe side.

DESCRIPTION OF EXAMPLE REALIZATIONS

In FIG. 1 is thus shown a known coupling 1 in an application. A bonescrew 2 of titanium is threaded and healed into the skull 3 of apatient. In the bone screw 2, which has an internally threaded hole inits center, a spacer 4 is screwed tight and on its outer end is mounteda ball-shaped coupling part 5. Also the spacer 4 is made of titanium andextends from the bone screw 2 out through the skin 6. On the ball-shapedcoupling part 5 a transmitter 8 is mounted via a cup-shaped couplingpart 7, which transducer contains for example a microphone, amplifier,vibrator and battery. The thus constructed coupling 1 has a number ofdrawbacks which were discussed above.

In FIG. 2a is shown a coupling according to the invention and mainly thepart that is to be mounted tightly in the skull of the patient. Thispart, which in the embodiment shown here consists of a first couplingpart 9, is screwed tightly by a mounting screw 10 in a bone screw 2 oftitanium in the same way as the known coupling. The bone screw is inturn surgically inserted into the skull bone of the patient, for examplebehind one ear. The first coupling part 9 contains mainly a cylindricalframe 11, equipped with a flange 12 at its upper end in which a frontplate 13 is mounted tightly via for example two screws 14. The plate 13can of course be mounted by other means such as glueing, riveting or thelike. In the plate 13 is mounted a downward narrowing cup-formed part15, in the center of which a rectangular volume 16 is made, and in whichcup-shaped part 15 a second coupling part 17 can be inserted. Around thevolume 16 in the cup-formed part's 15 bottom a circular path 18 isformed in which two grooves 19 are arranged opposite one another inwhich corresponding raised parts on the second coupling part 17 glidedown on locking the coupling. The coupling parts are thus arranged to belocked to each other through rotation of either of the coupling parts,for example through a quarter turn, in relation to the other couplingpart.

In the cylindrical frame 11 an active element 21 which is movable in theaxial direction, under the front line, that is in an imaginary line atthe same height as the plate 13 or the coupling part's outer surface 20,and a fastening element 26, made for example of tough plastic, arearranged. By active element 21 is meant here an arrangement whichapplies a mostly constant force which presses the coupling's 1 first andsecond coupling parts 9, 17 against one another in their coupledposition. This force is strong enough that no distortion can occurbetween the coupling parts 9, 17. Because the active element 21, and forexample also the vibration transmitting surface, that is the surface orthe surfaces which are formed between the coupling parts 9, 17 and whosepurpose is to transmit sound in the form of vibrations, is arranged atthe level of or under the front line, the coupling's total physicalheight can be kept relatively low, and the coupling need not stick outunnecessarily outside the skin 6 but instead the front line of thecoupling will be mostly at the level of the skin's 6 outer surface 22.

The fastening element 26 is stretched, with its upper part containing agripping piece, through the volume 16 formed in the plate's 13 middle.The upper surface of the fastening element's gripping piece 23 is thusplaced at the level of the coupling's outer surface 20. The grippingpiece 26 which is mainly rotationally symmetrical, is equipped with aflange 24 at the bottom which forms a stop for the active element, anO-ring 21 of a flexible material, for example silicon rubber.

The upper stop or limit for this O-ring is formed by the plate's 13under surface.

In FIG. 2b the first coupling part 9 is shown from above so that thegrooves 19 in the plate 13 are clearly visible. The fastening element's26 upper part, which contains a gripping piece 23, is flattened on twosides partly to allow insertion in the second coupling part's 17gripping volume or chamber 25 and partly to keep the fastening element26 from rotating inside the coupling which would cause the fasteningpiece's 16 and the plate's 13 positions relative to one another tochange with the result that the coupling would be useless.

In FIG. 3a is shown transducer the second coupling part 17 which ismounted on the transducer. It is mainly rod-shaped and contains aninternal cylindrical hole 25. A mainly rectangular shaped opneing 27allows insertion of the fastener's 26 gripping pieces 23. On each longside of the opening are raised parts 28 arranged radially which glidewith their outer surfaces along a path 18 and down in the grooves 19 atrotating and locking the coupling. Thus an advantageous self-cleaning ofthe vibration transmitting surface in the coupling is obtained so thatmechanical contact can always be maintained.

FIG. 3b shows the outer end of the second coupling part 17 in such a waythat the opening 27 and the raised parts 28 are clearly visible.

FIG. 4a shows an alternative first coupling part 29 in which the plate's13 function is exchanged for a cylindrical internally arranged stop 31inside the frame 30. Neither is the frame 30 equipped with a flange 12above as no plate 13 with fastening screws 14 is used. Through thisarrangement the outer diameter of the coupling can be reduced further. Apacking 32 of for example silicon rubber is placed between the fasteningelement 34 and the bone screw 35 and is arranged to damp uncomfortablesnapping sounds which can be produced when the parts are coupledtogether and to allow for mounting the O-ring and locking it.

FIG. 4b shows the alternative first coupling part 29 from above so thatthe fastening element 34, the grooves 36, the glide path 37 and theupper part of the frame 30 are visible.

In FIGS. 5a and 5b are shown an additional embodiment of the couplingaccording to the invention including a second coupling part 38 and afirst coupling part 39. The second coupling part 38 consists of a plate40 to which a transmitter 8 can be attached, an axle 41 equipped with asquare part 42 arranged for coordination with a spring loaded pin 43placed in the first coupling part 39 and a flattened contact part 44.The first coupling part 39 consists of an outer frame 45 in which alocking cylinder 46 made of a tough plastic, a flexible packing 47, offor example silicon rubber, and an outer plate 48 and two spring loadedpins 43 through it and at a distance from each other. At the bottom thefirst coupling part 39 is further equipped with a screw 49, to the upperpart of which a raised contact surface 50 is attached. The screw 49 ismounted in the same way as in the other described embodiment in a bonescrew 2 which is in turn surgically inserted in the skull 3 of thepatient.

On coupling the second coupling part 38 is pushed in through an oblongopening 51 in the first coupling part 39 until the second couplingpart's 38 contact surface 44a meets the first coupling part's 39 contactsurface 50. In that position the second coupling part 38 is rotated aquarter turn whereby the cone-shaped flattened contact surface 44 islocked by the locking cylinder 46 and held there in that position by thespring loaded pins 43 pressing against two sides of the second couplingpart's square part 42. Because the flexible packing 47 is pressedtogether on rotation a pressure is obtained on the locking cylinder 46which tries to press the second coupling part's 38 contact surface 44against the first coupling part's contact surface 50 whereby themechanical contact essential for transmission of the sound is maintainedbetween the two coupling parts.

In FIGS. 6a, b, c is shown a further embodiment of a coupling accordingto the invention. The first coupling part 52 consists, in the same wayas in the other embodiment, of an outer, mainly cylindrical frame 53equipped at its top with a flange 54. At the flange is a plate 55tightly attached with screws 56. Through the central part of the plate55, which has thicker material, passes the upper axle-shaped part of afastening element 57 which is adjustable in the axial direction andwhich is equipped with a recess 59 on one side. A packing 60, of forexample silicon rubber, is placed between the plate's 55 underside and aflange 61 attached to the fastening element's 57 lower part, whichflange applies a mainly constant force pushing away between thefastening element 57 and the plate 55.

In FIG. 6b the first coupling part 52 is shown from above so that it isseen how the hole 64 for receiving the second coupling part's 62coupling element 63 is shaped. At the bottom of that hole 64 is a groove65 arranged for locking the fastening element 63 of the second couplingpart 62 shown in FIG. 6c, which fastening element 63 mainly consists ofa circular axle in one end of which a recess 66 is arranged to fit therecess 59 in the fastening element 57. On coupling the first and secondcoupling part's 52,62 the second coupling part's 62 fastening element 63is inserted in the first coupling part's 52 hole 64 at such an anglethat the second coupling part's recess 66 is used so that its couplingpart 63 shall be free from the fastening element's 57 outer part. Whenthe second coupling part's 62 fastening part 63 has reached the bottomof the hole 64 the second coupling part 62 is bent back so thatpractically no angular difference remains between the first- and secondcoupling part's central axle. Thereby the hooks formed by the holes gripinto each other and as the active element and the packing 60 thus presstogether a mainly constant pressure is obtained which continuouslypresses down the point of the second coupling part's 62 coupling element63 in the groove 65 in the hole 64 which consequently locks the secondand the first coupling parts 62, 52 to each other.

Using the above described couplings according to the invention a numberof advantages are achieved compared to known technology. Above all acoupling with a low profile is realized which makes it estheticallyattractive and insensitive to blows and hits. The coupling is not in theway during sleep and clothing does not snag in it as easily. Thecoupling cannot unscrew itself either through rotations made by thetransmitter or the active element. The coupling is further angle stable,that is because the second coupling's raised parts snap down into thefirst coupling part's grooves a stable neutral position is obtained.

In FIG. 7a is shown an embodiment of a coupling according to theinvention which is relatively easy to disassemble and therefore easilyserviced. In the usual way the coupling is limited at the sides by arotation symmetric frame 70 in the bottom 71 of which is arranged a holefitting a bone screw 2. The frame's 70 encompassing walls limit a volume73 placed inside the first coupling part 77. This volume 73 has anopening pointed away from the coupling part's 77 bottom. On the insideof the frame 70 is a groove 78 placed near the edge of the opening. Thisgroove 78 is arranged to hold a flexible element, an O-ring 74 forexample of silicon rubber, in position. A spacer 79, for example made ofplastic, also equipped with a groove 80 around its perifery, is placedin the volume 73. The spacer 79 is placed in the volume 73 so that thespacer's 79 outer limiting surface 75 mainly coincides with thecoupling's outer limiting surface 20. The O-ring 74 allows the spacer 79certain mobility for action against a force.

In FIG. 7b the form of the spacer 79 is shown in greater detail. Arectangular opening 81 stretches axially through the spacer 79 to allowinsertion of a second coupling part 82. In the bottom of the spacer 79countersunk edges 84 are placed in conjunction with the hole 81 to allowrotation, a quarter turn, and locking of the coupling parts to eachother. On rotation of the coupling the spacer 79 is moved a littleoutward axially whereby a force pressing the coupling parts together isactivated by the O-ring's 74 flexibility.

The spacer 79 is further equipped with a locking groove 83 arrangedacross the hole 81. When rotation of the second coupling part iscompleted a quarter turn the spacer 79 is pushed down and the secondcoupling part 82 grips the locking groove 83. Through action of theO-ring 74 the coupling parts are held in this "locked" position until aforce stronger than that which locks the parts acts on one of thecoupling parts.

In FIG. 7c is shown the second coupling part from the side. Here it isclear that it consists mainly of a contact piece 86 placed on theextreme end of a mainly round axle 85. The contact piece's 86 downwardpointing surface is arched among other things to make the coupling "selfcleaning." The upper side of the contact piece 86 also has a slightlyarched surface which makes rotation and gripping the locking groove 83easier.

Through the construction of the described coupling parts and the activeelement a coupling is achieved with a long mechanical life which is alsoinfluenced by the coupling together being a rotation movement instead ofa simple "snapping mechanism" which is the case for the known coupling.The snap in such a locking mechanism which occurs at the moment oflocking and which is uncomfortable for the patient is also avoided.Locking through a rotation movement also protects the sensitivevibration element of the transmitter to which the second coupling partis mechanically attached.

If the transmitter is exposed to loads in the form of hits or bumps, oris overloaded in some other way, it is necessary that the coupling iseasily broken, which otherwise could lead to serious consequences suchas cracking the skull around the bone screw or the like. Through theconstruction according to the invention with the second coupling partonly somewhat inserted in the first coupling part and in which thefastening element is made in plastic the grips/flanges are dimensionedso that they shall give way at a given previously determined load.Neither does a disadvantageous lever effect occur, partly because thefirst coupling part's upper part is shaped with partly skew surfaces.This loading limit can be adjusted, in addition to through appropriatechoice of material and dimensioning of the gripping flanges thickness,through arranging grooves in the fastening element's upper part whichmake the gripping flanges give way.

The invention is naturally not limited to the embodiments describedabove, but instead a number of alternative embodiments are possiblewithin the scope of the invention.

I claim:
 1. Coupling, primarily intended for mechanical transmission ofsound information from a vibration generating apparatus such as atransducer (8) to the skull of a hearing impaired person, comprising afirst coupling part (5,9,29,39,52), tightly anchored in the skull, and asecond coupling part (7,17,38,62) attachable to said first part andarranged at the transducer (8), so that at least one vibrationtransmitting surface is formed between the coupling parts, wherein thevibration transmitting surfaces (18,50) are located inside the outersurface (20) of the first coupling part (9,29,39,52), and said firstcoupling part (9,29,39,52) is disposed in such a way that the outersurface thereof (20) is located essentially at the same level as theouter surface (22) of the skull.
 2. The coupling according to claim 1,wherein the first and the second coupling part are arranged to lock toone another so that one for the coupling part is rotated at a quarter ofa turn in relation to the other coupling part.
 3. The coupling accordingto claim 1, wherein an active element (21) is located inside the outersurface (20) of the first coupling part (9,29,39,52) and arranged toapply a constant force in the axial direction of the coupling (1) insuch a way that the vibration transmitting surfaces (44,50) of thecoupling (1) are pressed against each other and arranged to apply aconstant axial force of the coupling (1) parts and thereby on thecoupling's (1) vibration transmission surfaces (18,28;44,50).